Performance - Introduction — Page 140, Lesson 168

Let's start with the very foundation of performance: the classification system. In the world of commercial aviation, we don't just talk about "aeroplanes" as one group. We split them into Performance Classes, and this classification dictates which certification standards they must meet and how their performance is regulated. This is the first thing you need to internalise. We have Performance Class A. This covers multi-engine aeroplanes powered by turbo-propeller engines with a maximum approved passenger seating configuration of more than 9, OR a maximum take-off mass exceeding 5700 kg. And it also includes all multi-engine turbojet powered aeroplanes. So, if it's a jet with more than one engine, it's Class A, regardless of size. Class A aeroplanes must abide by the Certification Specifications laid out in the document from EASA called CS-25. That's the certification standard for large aeroplanes. Next, Performance Class B. This is for propeller driven aeroplanes with a maximum approved passenger seating configuration of 9 or less, AND a maximum take-off mass of 5700 kg or less. Note the "and" there — both conditions must be met. Class B aeroplanes must abide by the Certification Specifications laid out in the document from EASA called CS-23. Then we have Performance Class C. These are aeroplanes powered by reciprocating engines — that's piston engines — with a maximum approved passenger seating configuration of more than 9, OR a maximum take-off mass exceeding 5700 kg. So Class C is the piston-engine equivalent of Class A in terms of size. Finally, there's the Unclassified class. This is given to those aeroplanes whose performance characteristic is unique and special performance consideration is required. For example, the Unclassified class includes supersonic aeroplanes and sea planes. Let me give you a quick way to visualise this. Think of the engine type first. If it's a multi-engine jet, it's Class A. If it's a multi-engine turboprop, look at the mass and seats: if mass is greater than 5700 kg OR seats are more than 9, it's Class A; if mass is less than or equal to 5700 kg AND seats are less than or equal to 9, it's Class B. If it's a piston engine, same size logic: mass greater than 5700 kg OR seats more than 9 puts it in Class C; mass less than or equal to 5700 kg AND seats less than or equal to 9 puts it in Class B. Now, why does this matter? Because any class of aeroplane operated in the public transport role must adhere to the operational requirements set out in EU-OPS 1. EU-OPS 1 prescribes a minimum performance level for each stage of flight for Class A, Class B and Class C aeroplanes. The certification and operational regulations together aim to achieve a high standard of safety that has kept air travel as the safest form of travel. Here's the key concept: to achieve the required safety standard, the aviation authorities have added a safety margin into the aeroplane performance data. The application of these safety margins changes the expression of the performance data. That's the whole point of this introduction — the performance figures you'll see in manuals aren't raw test data. They've been adjusted, with safety margins built in, to give you a certified, operational performance expression. That's what we'll be diving into as we go through this chapter.